Parametrisation of wet deposition in the SNAP atmospheric dispersion model

Parametrisation of wet deposition of radionuclides is considered a main contributor of uncertainties in atmospheric dispersion models employed within nuclear emergency preparedness and risk management. In order to reduce these uncertainties the current work aimed to improve the parametrisation of the Severe Nuclear Accident Programme (SNAP) dispersion model by implementing new codes for in-cloud and below-cloud wet scavenging processes. The new parametrisation was validated by comparing model outputs with the following observation data from areas affected by the Chernobyl accident: A gridded dataset of deposition in Europe, a recently digitised environmental monitoring dataset of soil deposition, and airborne surveys from two areas in Norway. Comparison with observations from Norwegian soil data showed improvements in normalised mean bias for the new schemes, while comparison with observations from Europe as a whole showed improvements in metrics factor 2, 5, and 10, Pearson correlation coefficients and normalised mean bias when compared to the original scheme in SNAP.